CDMS

This entry is a combined CDMS and JPL entry.
The latest combined fit has been reported by
(1) H. S. P. Müller, B. J. Drouin, and J. C. Pearson, 2009, Astron. Astrophys. 506, 1487.
This work provides new data in the 1.58 – 1.63THz region. Additional, extensive data between 91 ans 1192GHz were published in
(2) G. Cazzoli and C. Puzzarini, 2006, J. Mol. Spectrosc. 240, 153.
As in that work, additional data were taken from
(3) S. G. Kukolich, D. J. Ruben, J. H. S. Wang, and J. R. Williams, 1973, J. Chem. Phys. 58, 3155;
from
(4) S. G. Kukolich, 1982, J. Chem. Phys. 76, 97;
and from
(5) D. Boucher, J. Burie, J. Demaison, A. Dubrulle, J. Legrand, and B. Segard, 1977, J. Mol. Spectrosc. 64, 290.
The purely K-dependent terms were determined through ΔK=3 infrared loops from
(6) R. Anttila, V.-M. Horneman, M. Koivusaari, and R. Paso, 1993, J. Mol. Spectrosc. 157, 198.
The predictions should be reliable throughout with the exception of K=14 transitions between about J=36 and 48 which are perturbed by a weak resonant interaction with v₈=1.
¹⁴N hyperfine splitting may be resolvable at low values of J and possibly at the highest K. Therefore, predictions with hyperfine splitting have been provided up to J"=9 (184GHz). Note: The partition function does not include the spin-multiplicities of ¹⁴N ! Therefore, partition function values have to be multiplied by 3 when considering ¹⁴N hyperfine splitting ! Vibrational contributions have been considered in the calculation of the partition function for states up to about 1200cm^–1. Higher vibrational states contribute to less than 1 % each at 300K. Values for the ground state are given in parentheses. Additional information on vibrational states is also available.
At low temperatures, it may be necessary to discern between A-CH₃CN and E-CH₃CN. The A state levels are described by K=3n, those of E state by K= 3n±1. The nuclear spin-weight ratio is 2:1 for A-CH₃CN with K>0 and all other states, respectively. The J_K=1₁ level is the lowest E state level. It is 5.5803cm^–1 above ground.
Nov. 2010: separate E and A predictions are available along with separate E and A partition function values. NOTE: Before any analyses are performed treating E and A states separately the effects of optical depth ought to be evaluated carefully !
The dipole moment was determined by
(7) J. Gadhi, A. Lahrouni, J. Legrand, and J. Demaison, 1995, J. Chim. Phys. 92, 1984.